The present invention relates to a feature detection apparatus and method for measuring structures of an object, and in particular, to a feature detection apparatus and method for measuring structures, such as diffuse reflective structures.
Optical instruments, such as surveying instruments are commonly used for distance measurement and comprise a complex arrangement of optical and electronic elements.
In recent years, imaging devices have been integrated in surveying instruments providing digital video data of an object in addition to distance measurement information. The imaging and distance measurement information may include horizontal and vertical angles, a distance to the object and an image of the object revealing its structures. This information may then be used to create a three-dimensional representation of the object.
However, due to the advancement of technology, a vast amount of data can be obtained through imaging and distance measurements, which has to be processed and analyzed correctly.
Several ways have been proposed to acquire an image with an optical instrument and at the same time measure the distance to each pixel in the image, for example, by sequentially scanning and measuring each position corresponding to a point in a three-dimensional grid.
For example, optical surveying instruments with imaging, direction and distance measuring capabilities with a fast rotating polygon mirror for laser beam deflection have been proposed, wherein a laser beam is scanned over an object, while a distance to a position on the object is measured and the horizontal and vertical angles to the position on the object with respect to the mirror position of the instrument are recorded.
Alternatively, an image may be recorded with a camera in advance and positions corresponding to the pixels in the image may then be derived and measured separately by a distance measuring device.
In each of the above-discussed optical instruments a large amount of distance and angle information is obtained, wherein often the largest part of the data is of no real interest to the user, since it may not relate to the desired object or specific object feature to be analyzed. This part of information reduces the speed of the measurement and requires large processing power so that often real-time data processing is not possible.
This means that the user might have to transfer the recorded data to a separate computer and select the data of interest after data acquisition.
On the other hand, specifying the data to be acquired in advance before data acquisition by the user may be time consuming and complicated, especially under field conditions, such as snow, rain and wind, where a fast automatic acquisition is preferable.